Diamantinasaurus is a genus of titanosaurian sauropod from Australia that lived during the early Late Cretaceous, about 94 million years ago.

The type species of the genus is D. matildae, first described and named in 2009 by Scott Hocknull and colleagues based on fossil finds in the Winton Formation.

AODF 603, the holotype, includes the right scapula, both humeri, right ulna, both incomplete hands, dorsal ribs and gastralia, partial pelvis, and the right hindlimb missing the foot.

[3] The paratype, under the same specimen, includes dorsal and sacral vertebrae, the right sternal plate now thought to represent the remainder of a coracoid, a radius, and one manual phalanx.

All these bones come from AODL 85, nicknamed the "Matilda Site" at Elderslie Sheep Station, located about 60 km (37 mi) west-northwest from Winton in central Queensland.

[9] In 2023, the fourth specimen, AODF 0906, consisting of a partial postcranial skeleton and a more complete skull with previously unknown numerous cranial elements intact has been described in detail.

[12] Since the original description, the only major revisions include the misidentification of the "sternal plate", misplacement of manual phalanges III-1 and IV-1 as III-1 and V-1 respectively, and the identification of the missing portion of the fibula.

Multiple other traits are found throughout derived titanosaurs, including downward angling of the skull, prong shaped lateral braincase processes, an undisturbed pituitary fossa, and a more centrally located opening for the internal carotid artery.

[7] Like more basal sauropods Europasaurus and Euhelopus, the dorsal vertebrae have a notch on the top of the posterior centrum face, giving it a heart-shaped appearance, contrasting more derived titanosaurs or Giraffatitan which possess flattened centra.

Although differing in centrum shape, Opisthocoelicaudia and Diamantinasaurus are the only titanosaurs to share a ventral keel set within a sharply defined depression under the dorsals.

A poorly preserved feature between the prezygapophysis and centrum may be the posterior centroprezygapophyseal lamina, found in some brachiosaurids, basal titanosaurs, and Opisthocoelicaudia.

The top edge of the ilium is broken, revealing numerous small internal camerae, as present in the titanosaurs Alamosaurus, Epachthosaurus, Lirainosaurus, Saltasaurus and Sonidosaurus.

Diamantinasaurus also displays the derived sauropod traits of a rounded ilium, reduced articular surface for the ischium, and a protuberance above the ischiatic articulation (only shared with Opisthocoelicaudia among Titanosauriformes).

The pubis, as in advanced sauropods, is a flattened bone, lacking the anterior hook of diplodocoids, but with potentially autapomorphic grooves surrounding the obturator foramen.

Diamantinasaurus also lacks a notable muscle scar for the M. flexor tibialis internus 3 on the side of the distal ischium, which is diagnostic for the taxon amongst Neosauropoda.

The crushing did not prevent the preservation of the linea intermuscularis cranialis ridge, also present in Saltasaurus, Neuquensaurus, Bonatitan, Rocasaurus and Alamosaurus.

A depression subdivides the fibular condyle, which bears a slight ridge also found in Magyarosaurus and other titanosaurs, although the prominence of it is unique to Diamantinasaurus.

The fibular condyle is larger than the tibial, and extends farther down, giving the femur a bevelled appearance, potentially diagnostic of Saltasauridae but also found in Rapetosaurus and the non-titanosaur Dongbeititan.

As in many titanosauriforms, the astragalus of Diamantinasaurus is less than 1.5 times as wide as long, and the proximal surface is divided into the ascending process and the fossa for the tibia.

[1] Chubutisaurus Wintonotitan Tendaguria Ligabuesaurus Phuwiangosaurus Andesaurus Argentinosaurus Epachthosaurus Malawisaurus Nemegtosaurus Diamantinasaurus Tapuiasaurus Alamosaurus Opisthocoelicaudia Isisaurus Rapetosaurus Trigonosaurus Saltasaurus Neuquensaurus In the same study, the relationships using the Mannion et al. (2013) matrix were tested.

[7][13] Andesaurus Dongyangosaurus Baotianmansaurus Ligabuesaurus Savannasaurus Diamantinasaurus Xianshanosaurus Daxiatitan Malawisaurus Muyelensaurus Futalognkosaurus Epachthosaurus Tapuiasaurus Nemegtosaurus Isisaurus Saltasaurus Opisthocoelicaudia Jiangshanosaurus Alamosaurus Gorscak & O'Connor (2019) in their description of Mnyamawamtuka recovered Diamantinasaurus as a saltasaurid using a parsimony phylogenetic analysis, while a variable-rates Bayesian phylogenetic analysis recovered it as falling just outside Saltasauridae.

[14] Karongasaurus Argentinosaurus Andesaurus Ligabuesaurus Jiangshanosaurus Angolatitan Malarguesaurus Chubutisaurus Wintonotitan Tastavinsaurus Malawisaurus Mnyamawamtuka Tapuiasaurus Normanniasaurus Rinconsaurus Isisaurus Rapetosaurus Muyelensaurus Bonitasaura Gondwanatitan Panamericansaurus Overosaurus Shingopana Trigonosaurus Aeolosaurus Argyrosaurus Diamantinasaurus Patagotitan Paralititan Maxakalisaurus Neuquensaurus Saltasaurus Epachthosaurus Futalognkosaurus Mendozasaurus Atsinganosaurus Notocolossus Rukwatitan Lohuecotitan Nemegtosaurus Lirainosaurus Opisthocoelicaudia Ampelosaurus Mansourasaurus Paludititan Pellegrinisaurus Dreadnoughtus Alamosaurus Baurutitan The 2021 study recovered a similar topology, finding a close relationship with Savannasaurus as well as Sarmientosaurus from the early Late Cretaceous of Patagonia, which skull had similarities to the referred cranial material of Diamantinasaurus.

The Winton Formation had a faunal assemblage including bivalves, gastropods, insects, the lungfish Metaceratodus, turtles, the crocodilian Isisfordia, pterosaurs, and several types of dinosaurs, such as the aforementioned Australovenator, the sauropods Wintonotitan, Savannasaurus, and Austrosaurus, and unnamed ankylosaurians and hypsilophodonts.